A scanning electron microscope (SEM) which is one of charged particle instruments accelerates electrons emitted from an electron source, and converges the electrons by an electrostatic or electromagnetic lens to irradiate a surface of a sample therewith. The electrons are referred to as a primary electron-beam. Secondary electrons are generated from the sample by the irradiation of the primary electron-beam. An amount of generating the secondary electrons is increased at an edge portion of a sample pattern. Therefore, a secondary electron signal intensity is acquired by scanning the primary electron-beam on the surface of the sample by an electromagnetic deflection. Then, an electron microscope image (SEM image) reflecting a shape of the sample is obtained. Such an SEM can observe a fine pattern by converging the primary electron-beam to be small. Therefore, the SEM is used for measuring a dimension of a fine circuit pattern in a semiconductor fabricating process.
In SEM, ordinarily, a landing angle of a primary electron-beam relative to a sample is perpendicular in a case of no deflection. On the other hand, in a case of deflection, generally, a trajectory of a primary electron-beam is changed and the landing angle is changed. When the landing angle differs, even when an image of the same sample pattern is acquired, a way of looking of a pattern is changed, and a critical dimension (CD) is changed. In addition, when a primary electron-beam is deflected, deflection aberrations of field curvature, astigmatism, coma aberration, distortion, chromatic aberration and the like are generated. The critical dimension is changed also by blurring or distorting an image by the deflection aberrations.
In measuring a dimension of a semiconductor circuit pattern, there is requested a high CD reproducibility less than 1 nm. In order to ensure the high CD reproducibility, a deflection region of a primary electron-beam is restricted to be less than, for example, 5 μm such that a change in the CD caused by the deflections is not manifested. On the other hand, there are increased a number of cases where the measurement is needed at a number of portions in the same sample. It is requested to increase a throughput by reducing a frequency of moving a stage for moving a field of view by scanning a wide region by deflecting the primary electron-beam. In order to realize compatibility of the CD reproducibility and the throughput as described above, it is necessary to enable to use a wide deflection region by restraining a change in the critical dimension (CD) caused by the deflection.
With regard to the problem, Japanese Unexamined Patent Application Publication No. 2006-173035 discloses a method of correcting field curvature, astigmatism, and distortion caused by deflecting a primary electron-beam. Also, Japanese Unexamined Patent Application Publication No. 2007-187538 discloses a method of making a landing angle equal in a deflection region.